Certain temperature sensors failing

The other day my Macbook Air crashed and when it rebooted, it was mega slow and the fan was permanently running.

I checked the processes and kernel_task was running at 300%. I reset the SMC and NVRAM, but this didn’t make a difference.

Apple diagnostics showed a problem with the PMC and SMC. I ran ASD EFI and this came back fine, but ASD OS came back with a bunch of sensor failures (unable to read).

I then stripped down my Macbook and gave it a good clean, removing dust from the SMC and then using isopropyl alcohol to clean it. When I rebooted, it looked like it was fixed. But 30 mins later, the same problem.

I installed iStats and this showed that certain sensors weren’t reporting. The strange thing is that it was occurring intermittently because the sensors would suddenly start reporting again. The failing sensors were:

• CPU Proximity, Camera Proximity, Charger Proximity, Inlet, Platform Controller Hub.

Can anyone advise where they think the problem might lie?